MAP Kinase Mediates Epidermal Growth Factor- and Phorbol Ester-induced Prostacyclin Formation in Cardiomyocytes

We studied the role of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) in epidermal growth factor (EGF)-induced prostacyclin (PGI2) production in cultured, spontaneously-beating neonatal ventricular rat cardiomyocytes. To this purpose, the effect of EGF on cardiomyocyte MAPK phosphorylation, MAPK activity and PGI2-production were investigated, and compared to those induced by the PKC activator 4βphorbol 12-myristate 13-acetate (PMA). Both EGF (0.1μ ) and PMA (0.1μ ) induced the rapid and reversible phosphorylation of 42 KDa-MAPK in ventricular cardiomyocytes, responses that were accompanied by transient increases in MAPK activity (190–230% of control values within 5 min), and two- to three-fold increases in PGI2formation. The tyrosine kinase inhibitors lavendustin (1μ ) and genistein (10μ ) strongly inhibited EGF-induced MAPK activation and PGI2-formation, but had no effect on PMA-stimulated responses. Experiments with the PKC inhibitor CGP 41251 (1μ ) or with PKC-downregulated cells demonstrated that in contrast to the PMA-stimulated responses, EGF-induced MAPK activation and PGI2-production were PKC-independent processes. Investigating the role of MAPK in EGF- and in PMA-promoted PGI2-formation, we found that the MAPK-inhibitor 6-thioguanine (500μ ), as well as the MAPK-kinase-inhibitor PD98059 (50μ ) abolished both EGF- and PMA-stimulated PGI2-production in cardiomyocytes. Our results indicate that MAPK-activation is at the basis of both growth factor receptor and PKC-dependent eicosanoid-formation in ventricular cardiomyocytes, where EGF-induced prostaglandin-production takes place via a PKC-independent pathway.